Nightfall is basically Vampires v Werewolves v Hunters. In the nightfall world there is permanent darkness and moon so vampires and werewolves can be out all the time. Basically the world is FUBAR. For the purpose of playing in it, it could be like that, or just rubbish weather (Twilight), only taking place at night (Underworld) or some other reason for only worrying about the sun where neccesary.
For the initial thoughts Try This.
Rules : Marvel Heroic Standard. (aka Cortex + Heroic Roleplaying)
Affiliations – Normal TBS
Distinctions – 3
Powers – 2 sets (or 3 for Weres)
Specialities – d6 (Trained), d8 (Expert), d10 (Master) – The only variation from the norm.